1. Field of the Invention
The present invention relates to a photoconductive device which can be used as a device for generating an electromagnetic wave in the frequency range of 30 GHz or more and 30 THz or less, i.e., in the frequency region from a so-called millimeter wave to a terahertz wave (which is also called a terahertz wave herein), and a method for producing the same, and apparatus using the same.
2. Description of the Related Art
In recent years, technological developments utilizing terahertz waves have become active. Japanese Patent Application Laid-Open No. 2002-223017 discusses a terahertz wave generating device. As shown in FIG. 10A and FIG. 10B which is a cross section view taken along line 10B-10B of FIG. 10A, the device includes a conductive portion 163 (163a and 163b) formed on a photoconductive portion 162 on a substrate 161 with the two sides separated from each other by a gap 165. One conductive portion 163a and the other conductive portion 163b of the conductive portion 163, which are separated by the gap 165, are disposed to have the gap 165 of about 5 μm. The photoconductive portion 162 often uses low-temperature-grown (LT-) GaAs with crystals grown in a temperature from 200° C. to 300° C. Applying a voltage of about 10 V to the conductive portions 163a and 163b and irradiating the gap 165 with a pulsed laser (its pulse time width being about 100 fs) generates a pulsed terahertz wave. The photoconductive portion 162 and two electrodes (the conductive portion) 163 together are also called a photoconductive antenna.